Some ingredients used in topical products are potentially irritating, especially to people with "sensitive skin."
As an example, hydroxy acids (HAs) and retinoids have been proven to deliver cosmetic benefits, such as improvement in the appearance of photodamaged or naturally aged skin, skin lightening, treatment of age spots, etc. Unfortunately, their use at high concentrations may occasionally be associated with skin irritation, e.g. skin redness and stinging sensation upon application. The irritation can be ameliorated by lowering the amount of an active ingredient in the composition or by reducing the active's penetration through the skin. A serious drawback of both approaches is that the efficacy is impaired. The HA related irritation can be reduced by raising the composition's pH but this method yields reduced efficacy due to a decreased HA penetration through the skin. It is desirable to reduce or eliminate the irritation potential of HAs and/or retinoids while maintaining their efficacy.
The occurrence, frequency and nature of irritation often varies from user to user. The severity of irritation to the susceptible user may range from mild to severe. Typical symptoms of irritation include itching (pruritus), stinging, burning, tingling, "tightness," erythema (redness) or edema (swelling).
Environmental conditions such as sunlight, wind, cold temperature and dry air, may cause or exacerbate the irritation. Additionally, soaps, detergents, cleansing products, shaving creams, alcohol and other products which remove some of the skin's protective lipids and/or secretions may increase the skin's permeability and sensitivity to topically-applied chemicals which would otherwise not produce irritation.
Similarly, the skin may become irritated due to infection, shaving abrasion, repeated or excessive washing or bathing, sun exposure, or other mechanical abrasion or injury.
In addition to chemical and environmental causes of skin irritation, many people have an inherent sensitivity or genetic predisposition to skin irritants ("intrinsic skin irritation"). Whatever the exact cause of irritation, many attempts have been made to reduce the irritation potential of topical products by identifying chemicals which tend to cause irritation and reducing their concentration or eliminating them from the products.
Unfortunately, it is often not feasible or practical to identify or eliminate all of the irritating chemical(s), particularly when the irritating chemical(s) are the active ingredient of the product or are required for formulation, preservative or other functional reasons.
The need exists, therefore, for a composition and method that prevents or reduces the skin irritation.
Van Scott et al. teach in numerous patents (e.g., U.S. Pat. No. 5,654,340; U.S. Pat. No. 5,677,340; U.S. Pat. No. 5,385,938 and U.S. Pat. No. 5,091,171) cosmetic compositions containing alpha-hydroxy acids, which may be present as lactones. Gluconolacone and glucarolactone (a.k.a. "saccharic acid lactone") are mentioned. Other lactones, however, which do not reduce irritation (see Example 1 below) are also mentioned. Van Scott et al. do not teach the use of any of the lactones for controlling or alleviating skin irritation
A commercially available product line "Exuviance" includes several products with gluconolactone. For instance, Exuviance Fundamental Multiprotective Day Creme SPF 15--Sensitive Formula includes gluconolactone. The Exuviance product information insert describes gluconolactone as a poly hydroxyacid and teaches that poly hydroxyacids are more gentle to the skin than hydroxy acids. One of the Sensitive Formula products is described as a "soothing toning" formula. It is clear from the product information insert that gluconolactone is included in the formula as an anti-aging ingredient, as a less irritating alternative to a hydroxy acid. The product includes traditional soothing ingredients, e.g. aloe vera extract, further indicating that gluconolactone itself is not included as an anti-irritant. The insert does not teach the use of gluconolactone for treating skin that is already irritated.
Another Exuviance product, Exuviance Essential Multi-Defense Day Creme SPF 15, includes gluconolactone in combination with glycolic acid. Again, the product does not describe the use of gluconolactone for alleviating or controlling any skin irritation or skin irritation that may be caused by glycolic acid. Indeed, gluconolactone is used in the amount that appears insufficient to alleviate irritation.
In the Exuviance products, gluconolactone is included as an less irritating alternative to an anti-aging ingredient, a hydroxy acid. The Exuviance product does not employ gluconolactone as an anti-irritant and the product information insert does not teach that gluconolactone is an anti-irritant. By contrast, the present invention is based at least in part on the discovery that gluconolactone lowers the irritation of an already irritated skin and prevents irritation that may be caused by topical cosmetic product application.
Furthermore, prejudice exists against using gluconolactone as an anti-irritant, since gluconolactone is considered in the art as an irritating ingredient, albeit less irritating than a hydroxy acid. See for instance Hahn et al (U.S. Pat. No. 5,716,625) column 2, lines 44-59, which lists gluconolactone as a chemical which "may cause the skin to become more sensitive to irritation triggered by other topically-applied chemicals . . . " It is, therefore, surprising and unexpected that gluconolactone acts as an anti-irritant on an already irritated skin and was able to reduce irritation associated with the use of skin care cosmetic compositions.